Modern electronic circuit design relies heavily on the use of digital components. Digital circuits can typically be designed, integrated and manufactured with greater predictability and accuracy than analog circuits. Moreover, modern fabrication techniques make the production of digital circuits straightforward and relatively cost-effective.
Nevertheless, certain electronic applications still require the processing of analog signals. For example, audio and video processing often relies on the processing of a received analog signal and the provision of an analog output signal.
To take advantage of digital design and fabrication techniques, such circuits may be implemented using a mixed digital/analog design. Typically, in such mixed circuits, received analog signals are converted to digital format. Signal processing is performed in the digital domain and the resulting processed digital signal is converted again to an analog output. In this way, the predictability and fabrication ease of digital signal processing cores may be combined with conventional digital to analog and analog to digital converters in order to perform sophisticated signal processing on analog signals.
Integrated mixed signal circuits are, for example, commonly used in television and radio receivers, audio devices, cellular (in particular 3G) telephone, and in power over Ethernet applications. A particular example of a mixed signal circuit is contained in U.S. Provisional Patent Application No. 61/294,092 that discloses a television tuner, for use in a television, personal video recorder, set-top box or the like.
Such mixed signal designs must often be tested to ensure design and/or production quality. To this end, such circuits may be superficially tested, by applying power and measuring a response to an input signal. More sophisticated tests may be performed by applying a known analog signal to the circuit input and measuring the quality and characteristics of the analog output.
Naturally, superficial testing may not diagnose imperfections. The more sophisticated tests require relatively complex analog signal detection equipment and an analog source. This makes integration of testing circuitry as part of the mixed signal integrated circuit cumbersome.
Accordingly, there is a need for an improved method of testing mixed signal circuits and, more particularly, integrating components allowing on-chip testing and self-testing of such circuits.